Data Sources: Several sources of data were used for the site-specific data: International Station Meteorological Climate Summary (ISMCS) data from the National Climatic Data Center (NCDC), the Solar and Meteorological Observing Network (SAMSON) data from NCDC, and the Integrated Surface Hourly Observations (ISHO) from NCDC. Although SAMSON (30 years of data) was used for the bulk of data for many of the airports, SAMSON did not include data for approximately 20 of the airports. It was necessary to download data from ISHO for the remaining airports. The main data set developed from these sources was for a 30 year period (1961-1990).
Supplemental sources to look at scales larger than immediate airports included pilot reports, sigmets, and airmet-based climatology produced by a meteorologist at the Aviation Weather Center (AWC), and lightning data provided by a meteorologist at the Meteorological Diagnostics Laboratory (MDL). Lightning data were available only for the CONUS. Various icing and turbulence climatology studies performed at the National Center for Atmospheric Research (NCAR) in Boulder were also utilized.
Input of Factors to Produce the Climatology: CWSU MICs provided the weather element thresholds that were used to produce climatology for airport-specific significant wind, significant ceiling, and significant visibility. The FAA provided a list of the 68 busiest airports (31 rated as large, 37 as medium) in the U.S. and Puerto Rico, ranked according to air traffic. Input values for the weather element thresholds were submitted for 67 of the 68 airports (thresholds were not identified for San Juan). Standard data sets were used to produce climatology for thunderstorms, snow, and freezing precipitation. Climatologies for turbulence and icing were produced using results of previous studies.
Viewing the Graphs and Results: After selecting an airport, clicking on one of the six specific graphs for an airport allows one to view the temporal distribution for a day in each of the seasons. Seasons are defined as follows: Spring: March-May, Summer: June-August, Autumn: September-November, Winter: December-February.
The significant weather frequency graphs are scaled so that the largest frequency for a particular element occupies approximately 90 percent of the vertical range of the y-axis of the scale. However, if the largest frequency for a factor is 1 percent or less, the maximum value on the y-axis is 1 percent.
The graphs allow one to quickly view distributions of significant weather factors at the 68 airports. To view detailed values, download the file for the airport. To view rankings according to any one factor, use the Aviation_Weather_Factor_Summary file. Complete summary tables for frequencies, including those weighted for air traffic and impact (according to input from the CWSU MICs) are contained in the Aviation Climate Assessment Word document. These summary tables should be viewed as tools for the team's use.
Interpreting Graphs: When you click on an airport, you will see six graphs that show frequency by season for: Significant wind, thunderstorms, significant ceiling, significant visibility, snow and freezing precipitation. For wind, visibility, ceiling, snow and freezing precipitation, these frequencies represent the percent of hourly observations in which the event occurred over the 30 year period of records. For thunderstorms, there are two bars for each season. The first bar shows the seasonal frequency of hourly observations in which thunderstorms were reported by a human observer at the airport. The second bar shows an approximated frequency (based on lightning data) of having at least one thunderstorm within a 50 nautical mile radius of the airport.
By clicking on any one of the six graphs, you can access the daily distribution of that event for the four seasons. The thunderstorm distributions show 3-hourly frequencies of having at least one thunderstorm within 50 nautical miles (blue), as well as the hourly frequencies based on human observer-reported thunderstorms at the airport (brown).